Tone control



A. C. MILLER TONE CONTROL low 28, 1.939.

'Filed May s, 193e Patented Nov. 2s, 1939 I 2,181,817

UNITED STATES PATENT OFFICE TONE CONTROL Ambrose C. Miller, Jenkintown, Pa., assignor to Philco Radio & Television Corporation, Philadelphia, Pa., a corporation of Delaware Application May 8, 1936, Serial No. 78,702 In Great Britain May 25, 1935 3 Claims. (Cl. 179-171) This invention relates to tone control devices and its other extremity connected to the anode for radio receivers by which the tone quality of supply and through a by-pass condenser to the reproduced sound may be varied as desired. ground. A second resistor R2, constituting the Theprincipal object of the invention is to progrid resistor of tube V2, may have one extremity 5 vide a circuit for a tone control device of the type connected to the grid of that tube and its other having several adjustable positions, which is genextremity connected to a grid-biasing source. erally superior to prior circuits of this class and The Erst-mentioned extremities of these two re- Which is a marked improvement by virtue of the sistors may be connected through a coupling elimination of the annoying clicking sound which condenser C1.

accompanies adjustment of prior multipoint de- The tone control device TC may comprise a l0 vices as used. plurality of condensers, each having one terminal Generally speaking, a tone control device comconnected to a common point, while the other prises a group of condensers and switching means terminals of the condensers are connected rearranged so that the condensers may be selecspectively to stationary switch contacts. A movtively included or excluded from the receiver cirable switch arm may be arranged to engage the 15 cuit. Heretofore, the tone control device has been stationary contacts, so as to include one of the connected in the plate or anode circuit of an condensers in circuit or several of them in parallel audio-frequency amplifier with one terminal of relation. the device connected to the anode of the amplifier In accordance with the invention, the common 0 and with the other terminal connected to ground terminals of the condensers, as above mentioned, 20

or alternatively to the anode supply circuit. In may be connected to a point P of the receiver cirsuch arrangements, the condensers of the tone cuit between the coupling condenser C1 and the control device are connected directly in circuit grid resistor R2. The movable switch arm S of with the amplifier tube or with the plate resistor the tone control revice may be connected directly comprising an element of the conventional reto a suitable point of the grid resistor R2 and 25 sistance-capacitance coupling. In either case, the may be connected also to ground through an advcondensers of the tone control device are subject ditional condenser C2. In the speciiic embodito a charge which has a constant component due ment illustrated, the tone control device comto either the voltage drop across the tube or the prises three condensers C3, C4, and C5 connected voltage drop established across the plate resistor respectively to stationary contacts 3, 4 and 5 of 30 by the direct current component of the plate curthe group of contacts numbered respectively from rent. In either case, when the tone control del to 5. By this arrangement, the switch arm S vice is adjusted from one position to another, has four selectable positions, in each of which the one or more of its condensers is suddenly either arm is bridged across two contacts. In the rst charged or discharged and this charging and disposition with the switch arm bridged across con- 35 charging of the condensers causes the undesirable tacts l and 2, the condensers are disconnected clicking sound. from the circuit. In the second position with the In accordance with the present invention, the switch arm bridged across contacts 2 and 3, Cs tone control device is located so that it funcalone is connected in the circuit. In the third tions eiciently, and at the same time, the obposition with the switch arm bridged across con- 40 jectionable charging and discharging of the contacts 3 and 4, the condensers Cs and C4 are con, densers is avoided and the undesirable clicking nected in parallel to the circuit. In the fourth sound is eliminated. The invention may be position with the switch arm bridged across conunderstood by reference to the simple emboditacts 4 and 5, the condensers C4 and C5 are conment illustrated on the accompanying drawing, nected in parallel to the circuit. It will be under- 45 the single gure of which is a schematic illusstood, of course, that other arrangements of tration of a portion of a radio receiver embodycondensers may be used. ing the invention. Thus, the grid resistor R2 or a portion thereof Referring to the drawing, a conventional vacmay be shunted by a capacitance whose value deuum tube V1, functioning either as a detector or pends upon the position of the switch arm. Since 50 as an audio-frequency amplifier, is coupled by the the grid of the biased amplifier V2 does not norconventional resistance-capacitance coupling to mayy draw current, no unidirectional voltage will an audio-frequency amplifier V2. The coupling be developed across the the grid resistor R2 and, may comprise a plate resistor R1 having one extherefore, the condensers C3, C4 and C5 will not 5 tremity connected to the anode of the tube V1 be subjected to a unidirectional ,charging voltage 55 and will not charge and discharge as the tone control device is adjusted from one position to another. Similarly, the condenser C2 is prevented from charging and discharging. As the tone control device is isolated from the plate circuit of the tube V1 by the coupling condenser C1, the objectionable charging and discharging of the tone control condensers is completely eliminated, as is also the undesirable clicking noise. It will likewise be noted that the resistance R2 and condenser Cz constitute a filter for the grid bias supply.

Although the invention has been illustrated and described with specic reference to a pre-V ferred embodiment, it will be understood that modications or changes are possible Without departing from the scope of the invention.

I claim:

l. In a radio receiving system or the like, a space discharge device having an anode, an energizing circuit for said anode including a source of unidirectional potential, signal transfer means including a condenser connected to said anode and to said energizing circuit, a second space discharge device having a control grid and a cathode, means connecting said control grid to said signal transfer means, a grid resistor connected to said control grid, a source of grid-biasing potential connected between said resistor and said cathode so as to bias said grid negatively to prevent ow of unidirectional current thereto during normal operation of said second device, a tone control device comprising a plurality of condensers and switching means for rendering one or more of said condensers eiiective, means connecting said tone control device directly across at least a portion of said grid resistor to the eX- clusion of said grid-biasing source, and a condenser connected between said tone control device and the positive side of said grid-biasing source.

2. In a radio receiving system or the like, a space discharge device having an anode, an energizing circuit for said anode including a source of unidirectional potential, signal transfer means including a condenser connected tolsaid anode and to said energizing circuit, a' second space discharge device having a control grid and a cathode, means connecting said control grid to said `signal transfer means, a grid resistor connected densers and switching means for rendering one or more of said condensers effective, and means connecting said tone control device directly across at least a portion of said grid resistor to the exclusion of said grid-biasing source.

3. In a radio receiving system `or the like, al

pair of successive vacuum tube stages coupled together by a resistance-capacitance coupling including a series coupling condenser anda shunt resistor connected to the input element ofthe later vacuum tube stage, a tone control device including a plurality of condensers and switching means for changing the capacity of said device, means connecting one terminalof said device tothe common connectionof said coupling condenser and said resistor, and means connecting the other terminal of said device to a point on said resistor, whereby said device is prevented irom charging or discharging during manipulation of said switching means.

AlvLBRosE C. MILLER. f 

